1. Field of the Invention
The present invention is related to trip unit housings for motor operators. More specifically, the invention relates to a motor operator housing having a sliding cover for the trip sensitivity adjustment screws, thereby providing the ability to gain or lock out access to these screws when a motor operator is installed.
2. Description of the Related Art
Although various means of selectively permitting and blocking access to the controls and adjustments of a circuit breaker to which a motor operator has been attached have been proposed, a means of selectively permitting and blocking access to the sensitivity adjustment screws of a circuit breaker, which are typically covered by the trip unit cover of the motor operator, is not addressed within any references known to the present inventors.
A typical circuit breaker includes two trip mechanisms. The circuit breaker will trip electromagnetically when an overcurrent condition generates a magnetic force, and toggles the trip mechanism. Additionally, a persistent overload, not large enough to instantly trip the breaker, will cause an increase in temperature within the circuit breaker, causing a bimetallic strip within the circuit breaker to bend until it reaches a point wherein the circuit breaker is tripped. The sensitivity of both the trip mechanisms may be adjusted by adjustment screws accessible from the face of the circuit breaker.
Circuit breakers are frequently actuated remotely, by securing a motor operator over the face of the circuit breaker, so that the motor operator can actuate the trip unit. A typical motor actuator includes an electric motor, operatively connected through a system of gears to a threaded rod. A sliding actuator is threadedly connected to the threaded rod, so that rotation of the threaded rod causes the sliding actuator to reciprocate back and forth. The sliding actuator fits over the circuit breaker""s operating handle, so that movement of the actuator moves the operating handle. A kill/toggle switch at each end of the sliding actuator""s range of travel shuts off the current, and reverses the direction of current that will be supplied to the motor, upon being depressed by the sliding actuator. A printed circuit board will typically contain the motor operator""s control circuitry. When the user transmits a signal to close the circuit breaker, the control circuitry will supply current to the motor, thereby rotating the threaded shaft to slide the sliding actuator from one end of its range of travel to the other, thereby moving the circuit breaker""s operating handle, and closing the circuit breaker. Upon reaching the end of its range of travel wherein the circuit breaker is closed, the sliding actuator hits the toggle switch at that location, thereby shutting off current to the motor, and reversing the direction of current to the motor. When the user opens the circuit breaker, the control circuit will again supply current to the motor, thereby moving the sliding actuator to the opposite end of its range of travel, moving the circuit breaker""s operating handle to its open position. As before, when the sliding actuator reaches the position wherein the circuit breaker is open, it strikes a kill/toggle switch, shutting off current to the motor, and reversing the direction of current flow to the motor.
U.S. Pat. No. 5,700,985, issued to K. M. Fischer et al. on Dec. 23, 1997, describes an electrical operator having an interlock latch. The latch includes a slider plate moving between a first position permitting electrical operation of the circuit breaker to which the electrical operator is connected, a second position permitting manual operation of the circuit breaker, and a third position blocking both manual and electrical operation of the circuit breaker.
U.S. Pat. No. 5,693,923, issued to L. Gula et al. on Dec. 2, 1997, describes a motor operator for electrical switches that is pivotally mounted so that it may swing between a closed position wherein the motor operator actuates the switch, and an open position wherein the switch may be manually operated.
U.S. Pat. No. 5,821,487, issued to D. H. Groves et al. on Oct. 13, 1998, describes a lock out mechanism for a circuit breaker, wherein the circuit breaker is locked in the off position when the enclosure within which the circuit breaker is contained is opened.
U.S. Pat. No. 5,905,239, issued to D. C. Turner et al. on May 18, 1999, describes a motor operator with a means for protecting the motor from burning. The carriage within the motor operator that drives the handle of the actuated device includes a releasably secured bracket, dimensioned and configured to actuate the on limit switch. Therefore, if the motor operator is used to actuate a circuit breaker that has not been reset, the bracket will remain in contact with the on limit switch when the circuit breaker trip switch and carriage return to the off position. The motor is thereby protected from burnout during repeated unsuccessful attempts to turn on the circuit breaker. A similar motor operator is described in U.S. Pat. No. 5,695,046, issued to D. C. Turner et al. on Dec. 9, 1997.
U.S. Pat. No. 6,239,676, issued to J. G. Maloney et al. on May 29, 2001, describes a two-pole circuit breaker providing access to the calibration slots when the circuit breaker is assembled.
U.S. Pat. No. 6,111,486 issued to K. M. Fischer et al. on Aug. 29, 2000, describes a lockout assembly for trip unit settings. The lockout assembly includes a slidably mounted plate having apertures for accessing the trip unit adjustments. The plate slides between one position wherein the adjustments are accessible through the apertures, and a second position wherein access to the adjustments is blocked. When access to the adjustments is blocked, a wire clip may be inserted through an aperture in the sliding plate, and a corresponding aperture in the sliding plate""s cover, thereby securing the sliding plate in this position.
U.S. Pat. No. 6,080,947, issued to P. L. Ulerich et al. on Jun. 27, 2000, describes an electrical switching apparatus, such as a circuit breaker, having a self-supporting operating mechanism module, and operating condition indicators mounted in its faceplate.
The present invention provides a sliding cover for the adjustment screws of a circuit breaker. The sliding cover may be used with either three-pole or four-pole circuit breakers, and may also include means for locking out access to the adjustment screws.
A typical three-pole circuit breaker includes two adjustment screws: one to adjust the sensitivity of electromagnetic tripping, and the other to adjust the sensitivity of thermal tripping. When a motor operator is mounted over the operating handle of a circuit breaker, to permit remote opening and closing of the breaker, the motor operator housing will typically cover these adjustment screws. It is therefore desirable to include apertures within the housing of the motor operator cover to permit access to these adjustment screws, and to provide a cover for selectively permitting and resisting access to the adjustment screws.
An adjustment screw cover of the present invention includes a plurality of snap-in tabs dimensioned and configured to mate with corresponding slots within the motor operator housing. The cover may therefore be installed on the housing by simply snapping it into place. Once installed, the snap-in tabs are slidably movable within the slots, thereby permitting sliding movement of the cover between an open position and a closed position.
When the cover is in the open position, apertures defined within the cover are aligned with the apertures defined within the motor operator housing, thereby permitting access to the adjustment screws through these apertures. When the cover is in the closed position, the apertures of the cover are not aligned with the apertures defined within the motor operator housing, thereby resisting access to the adjustment screws. Additionally, some embodiments may include at least one aperture within the cover, and a corresponding aperture within the motor operator housing, permitting a wire or other objects to be inserted through these pairs of apertures, thereby securing the cover in the closed position.
An adjustment screw cover of the present invention may be utilized with either three-pole circuit breakers, having two adjustment screws, or four-pole circuit breakers, having three adjustment screws. To accommodate both types of circuit breakers, the adjustment screw cover defines three apertures, with two of the apertures being located within the main portion of the cover, and the third aperture being located within a detachable third portion of the cover. If the cover is used with a four-pole breaker, the cover is used as is, with the end section in place. If the cover is used with a three-pole breaker, the end portion of the cover may be broken off, so that the cover contains only the two apertures required, without having excessive length.